It is known to provide ionizing electrodes with a conducting or insulating protective coating in order to prevent corrosion.
According to the German Pat. No. 368,519, insulating varnish or a coating of nonconducting enamel is applied to the ionizing or corona discharge electrodes of a dust-collecting electrostatic precipitator.
From the German Pat. No. 557,185 it is known to use an electrically conducting varnish, particularly a graphite-containing varnish, as a protective coating on the electrodes.
It is also known to coat corona discharge electrodes with varnish as well as with hard rubber or a phenol condensation product in such a manner that the edges of the corona wires are left by the protective coating.
These coatings are used to prevent corrosion mainly in wet-process electrostatic precipitators or in mist-collecting electrostatic precipitators. In most of such precipitators, deposited dust is rinsed from the corona discharge electrodes rather than being removed in that the electrodes are vibrated, shaken, or rapped. Rapping of such corona discharge electrodes involves the risk that the vibration of the wire may result in cracks in the relatively brittle protective coatings, and moisture diffusing into such cracks and corrosive gaseous constituents can migrate under the protective layers so that the metallic parts of the corona discharge electrodes are corroded and break.
Another disadvantage of such layers on ionizing electrodes, particularly of electrically insulating layers, resides in that they suppress the corona discharge so that the resulting ionization is reduced.